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A Positive View of Women’s Exercise, Menstrual Cycles and Ovulation

I believe that “athletic amenorrhea” is a myth! There are no negative effects related to exercise if women start exercising when their cycles are mature and ovulatory, if they are of normal weight and maintain it, if life stresses are not major, and if they begin and increase exercise sensibly. However, according to the American College of Sports Medicine (1) exercise causes some women to lose their menstruation, called amenorrhea, have eating disorders such as anorexia nervosa, and develop osteoporosis. These three make what is commonly called the “female athlete triad.” Yet, healthy exercise is not causally related to eating disorders, osteoporosis or loss of flow based on over 20 years of research we’ve performed on exercise, menstrual cycles and ovulation (2).

Why would something be commonly believed, touted by experts and yet be a fairy tale? Perhaps because exercise hasn’t traditionally been considered “lady like.” Sweating, after all, is not very feminine! The other reason is that studies have examined women at one point in time, which are called cross-sectional studies, rather than in studies over time called prospective. These cross-sectional studies compared exercising women that were skipping periods, too skinny or had a stress fracture with non-exercising women.

The only way to know for sure that there is a relationship between exercise and menstrual cycle, weight or bone changes is to start with women who are normal, add exercise to part of the group, and see what happens. Several studies have done this and shown no negative effects of exercise (2-4). However, some women do over-exercise as a way of dealing with major life stresses. Some women with strong eating concerns do use exercise as a way to keep their weight low, or even to try and prevent periods. And some skinny, exercising women do have very low bone density and break bones. Even worry about weight, in women of normal weight with regular cycles, causes increased stress hormone levels like cortisol (5), is associated with ovulation disturbances (6), and may cause negative bone changes (7).

In contrast to the negative concepts about exercise for women’s cycles, there are several ways in which exercising is positive for women’s hormones, health and bones. These ways include decreasing premenstrual symptoms, increasing bone density (8), controlling weight and preventing diabetes, preventing breast and uterus cancers, and decreasing the risks for heart attacks. I’ll describe each of these and provide the evidence.

One of the first things that I learned when studying women starting a very mild walking exercise programme was that their premenstrual symptoms decreased over only three months compared with a group not regularly walking (9;9). Women training for a marathon over six months compared with themselves and a non-exercising control group developed less fluid retention, less sore breasts and less depressive symptoms (10). These marathon-training women felt that outside stresses were less and their feelings of anxiety tended to decrease (10). Increasing exercise not only burns calories but takes away inappropriate hunger. Therefore, women who are regularly exercising are more likely to maintain a healthy weight (11). Research in our centre showed that initially ovulatory, normal weight women could train for and run a marathon and have no differences in their menstrual cycles and ovulation over one year compared with inactive women (4). Furthermore, women who were runners gained significantly more spinal bone, taking the positive effects of normal ovulation into account, than did women who were non-runners (8). Women who were athletic in university compared with those who weren’t, with both groups followed for about 20 years, have been shown to have lower risks for breast and other reproductive cancers (12), to be less likely to develop diabetes(13) or to have a fracture after 40 (14). The evidence about exercise and preventing heart disease is less clear in women than in men—however data do suggest that exercising women have fewer heart attacks than age- and risk-factor matched sedentary women (15).

Why would walking or starting a running programme alter premenstrual symptoms? I think it is because the brain-pituitary-ovary system adapts to exercise just like our muscles and our heart and lungs do. The result of that adaptation is that our ovaries make slightly lower the amounts of estrogen each cycle while continuing to maintain levels needed for ovulation. If exercise increases more rapidly, or there is weight loss, or the increasing exercise corresponds with emotional stresses, then ovulation will usually continue but the time from release of the egg until the next period will be shorter than normal. This is called a short luteal phase cycle and it occurs if the luteal phase time of high progesterone is less than 10 days as shown by quantitative basal temperature or less than 12 days by a urine LH peak test. The good news is that usually the luteal phase becomes normal again in a cycle or two—thus the changes of exercise are not a sign of disease but rather an adaptation (16).

The other confusing thing about exercise and women’s periods is that teenagers are likely to start exercise training around the time when their reproductive system is just maturing. If exercise begins heavily and is associated with weight loss in a girl who is before her first period, menarche is likely to be delayed. If exercise increases in the early years after menarche, periods are more likely to stop, probably because ovulation hasn’t yet become established and reproduction mature. All of this means that our menstrual cycles and ovulation are more likely to be disrupted by usual stresses when we are in our teens than they will be later.

In summary, exercise is healthy for women as well as for men. The changes in women’s reproduction and bone health are positive as long as exercise begins gradually, a healthy weight is maintained, and life stresses are handled by support and relaxation rather than compulsive exercise. For optimal bone health, cycles need to remain normally ovulatory, weight needs to be normal and steady and a woman needs emotional and social networks of support.

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Estrogen’s Storm Season: Stories of Perimenopause

by Dr. Jerilynn C Prior

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